1. Field of the Invention
The present invention relates to a thermosensitive recording medium which utilizes color-developing reaction between an electron-donating color-forming compound and an electron-accepting compound, and which is suitable for an image-forming sheet for medical use, especially for a diagnosis or reference of images by X-ray, MRI, CT, or the like.
2. Description of the Related Art
Conventionally, there have been widely known thermosensitive recording media having, on a support such as paper, a thermosensitive recording layer containing an electron-donating color-forming compound (hereinafter may be referred to as a “color former”) and an electron-accepting compound (hereinafter may be referred to as a “color developer”). In the thermosensitive recording media, the color-former is reacted with the color-developer for color development. Such thermosensitive recording media are advantageous in that the recording machine therefor is compact and inexpensive, and its maintenance is easy, and therefore are broadly used for facsimiles, vending machines, printers for scientific measurement, printers for printing POS-bar code, or printers for CRT medical measuring instruments.
Also, a thermosensitive recording medium using a white plastic film on a support has been widely known, which is used in various applications such as POS bar code, display for a card-type mobile phone, medical image formation, or sheet-form display capable of writing and deleting with a reversible thermosensitive recording medium.
With regard to the medical image forming sheet, since it is used for diagnosis or reference, the object of recording is mainly structural information or shape information of the internal organs or bones of human. Accordingly, it is important that the images recognized precisely reflect original shape information, and thus it is expected that the sheet is excellent in pure blackness, high gradation, and high glossiness of the images, and also excellent in graduation, contrast and the like.
Thus, especially in medical applications of a thermosensitive recording material, high graduation is required compared to the conventional leuco type thermosensitive recording medium, so that a recording of higher output is demanded. When a plastic film is used as a support, there is a problem that the electrostatic attraction of trash and dust causes image defects such as white spots on a halftone portion.
In addition, in view of the contrast and the handling, it is preferred that the recording material itself is highly excellent in whiteness.
Furthermore, when the product has a shape of sheet, there are problems such that sheets are attached together at the time of feeding, causing double feeding issue in conveying the photoprints, and that the output sheets are prone to be closely attached to each other and thus they are difficult to handle.
In view of these required quality, it is required that the surface opposite to that of the support of the thermosensitive recording medium (back layer) be white or transparent, and have antistatic property and anti-adhesion property.
Although inventions that solve some of these problems have already been proposed, none of these inventions solves all of the above-mentioned problems and accordingly, additional improvements are needed.
Examples of the related patent documents include Japanese Patent (JP-B) No. 3710832, Japanese Patent Application Laid-Open (JP-A) Nos. 10-090830, 2005-193564, 2006-82483, and 2006-82309.